A method of obtaining alcohols by reducing ketones, esters, and lactones is important in chemical synthesis. In terms of reduced by-product formation, good operatability, and work safety, etc., reduction by catalytic hydrogenation is useful as a method for production of alcohols. Further, optically active alcohols are important as physiologically active materials such as pharmaceuticals, agrochemical agents, and aromachemicals, etc. and also as their synthetic intermediates. Asymmetric hydrogenation of ketones or hydrogenation-reduction of optically active esters is useful as a method for production of optically active alcohols. Ruthenium complexes having polydentate ligands are one of such reducing catalysts.
As for the ruthenium complex having a tridentate ligand which contains two phosphino groups and a —NH— group, a dichloro complex is described in Patent Document 1. Further, in Non-patent Document 1, a dichloro complex or a hydride complex having a trimethyl phosphine as a ligand is described. However, these complexes do not have a carbonyl ligand. Further, although a ruthenium complex having a tridentate ligand which contains two phosphino groups and a pyridine ring and a carbonyl ligand has been reported in Non-patent Documents 2, 3 and 4, no —NH— group is contained in the tridentate ligand.
With regard to the ruthenium dichloro complex disclosed in Patent Document 1, it is reported that ketones are hydrogenated and reduced in the presence of a base to give alcohols. However, no description is included regarding the reduction of esters or lactones. The ruthenium phosphine complex disclosed in Non-patent Document 1 is reported as a catalyst for dehydrogenation of ammonia-borane. However, hydrogenation-reduction of ketones, esters, and lactones is not described. Further, as the ruthenium phosphine complex has been reported to be unstable, its industrial application is difficult due to disadvantage in handling. Further, although it has been reported that the ruthenium complex having a pyridine ring as disclosed in Non-patent Document 2 or Non-patent Document 3 can catalyze the hydrogenation-reduction of esters or the ester synthesis reaction based on dehydrogenation of alcohols, there is a problem in that not only low temperature is required for the synthesis of the complex but also complicate procedures and the radical reaction using a tin compound, which is undesirable in terms of industrial application, are used for the synthesis of the ligand, etc. In particular, because the ruthenium complex having a pyridine ring described in Non-patent Document 2 has low catalytic activity for hydrogenation-reduction of esters, development of a catalyst having higher catalytic activity has been waited for.